Study: Giant Carnivorous Dinosaurs were Optimized for Energy-Efficient Walking
Theropod dinosaurs were the dominant terrestrial carnivores during much of the Mesozoic era.
These dinosaurs ranged in mass from 200 g to 9,000 kg and occupied much of the available niche space.
While no single adaptation is likely to explain such widespread dominance and diversity of form, the bipedal locomotory system employed by theropods is invoked as an important reason for the success of this lineage.
Plenty of research has explored the relationship between their locomotion and lifestyle. Much of this work has focused on running speeds, but Dr. Alexander Dececchi of Mount Marty College and colleagues argue that speed might not be the most important factor, especially for the biggest theropods.
The researchers gathered data on limb proportions, body mass, and gaits of more than 70 species of theropod dinosaurs.
They then applied a variety of methods to estimate each dinosaur’s top speed as well as how much energy they expended while moving around at more relaxed walking speeds.
Among smaller to medium-sized species, longer legs appear to be an adaptation for faster running, in line with previous results.
But for the real titans, top running speed is limited by body size, so longer legs instead correlated with low-energy walking.
Running is important for hunters, but they generally spend much more time roaming around in search of food.
“While speed was a major advantage for dinosaurs who needed to hunt prey and also escape predators, the biggest theropods relied more on efficiency while foraging,” Dr. Dececchi and co-authors said.
“Among giant theropods, the champions were tyrannosaurs like T. rex, whose long legs were apparently well-adapted for reduced energy expenditure while prowling for prey.”
“Size matters. Smaller theropods were both hunter and the hunted, so their lives were lived at high speed. For giants like T. rex, a top predator with no natural enemies, life was a marathon not a sprint.”
T.A. Dececchi et al. 2020. The fast and the frugal: Divergent locomotory strategies drive limb lengthening in theropod dinosaurs. PLoS ONE 15 (5): e0223698; doi: 10.1371/journal.pone.0223698